1. Field of the Invention
The present invention generally relates to an organic electro-luminescent (to be abbreviated as “EL” hereinafter) device, and more particularly to an organic EL device provides increasing the number of moisture-absorbing channels to prevent the generation of dark spots and to improve the luminescence quality of the organic EL device.
2. Description of the Prior Art
The organic EL device has attracted tremendous attention due to its advantages over other display panels. These advantages include larger visual angle, shorter response time, smaller dimension in thickness, lower power consumption, simpler fabrication, no need for backlighting, and the ability for light emitting in a full color range.
Please refer to FIG. 1, which is a cross-sectional view showing the structure of a conventional organic EL device in accordance with the prior art. The organic EL device is characterized in that a bottom electrode 12 is formed on a substrate 11, and on the bottom electrode 12 there are an organic layer 13 comprising a hole injection layer, a hole transport layer, an organic emitting layer or an electron transport layer, an opposed electrode 14 and an sealing cap layer 15 formed by evaporation in turn. Since, in an organic EL device, the light is generated when the electrons and holes from the bottom electrode 12 and opposed electrode 14 combine in the organic layer 13 to excite the organic emitting layer, it is inevitable that heat is generated during the luminescence process. Once the heat encounters the moisture existing inside the sealing cap layer 15, dark spots due to oxidation will be formed on the surface of the organic layer 13. The existence of such dark spots adversely affects the luminescence quality such as luminescence intensity and luminescence uniformity of an organic EL device. More seriously, the lifetime of an organic EL device may be substantially shortened.
In order to overcome the image defects due to the undesirable dark spots, the industry has developed a number of prior art organic EL displays to improve the image quality. For example, in Japanese Patent Nos. JP-A-363890 and JP-A-5-114486, it is disclosed that liquid fluorinated carbon is disposed inside the sealing cap layer 15 to effectively remove the heat generated during the luminescence process. In Japanese Patent No. JP-A-5-41281, it is disclosed that dehydrating agents such as a synthetic zeolite are mixed in the liquid fluorinated carbon to effectively remove the moisture existing in the periphery of the device. Moreover, in U.S. Pat. No. 5,962,962, entitled “Method of encasesulating organic electro-luminescence device and organic electro-luminescence device”, it is disclosed that a silicone oil or a silicone grease is used as a protective liquid to remove the existing moisture.
The above prior arts can reduce the generation of dark spots to some extent; however, the dehydrating agents such as liquid fluorinated carbon may add difficulty to the fabrication process, which is unfavorable for fabrication integration and reduction in cost.
Accordingly, a second prior art structure of an organic EL device is proposed as shown in FIG. 2. In U.S. Pat. No. 5,882,761, entitled “Organic EL element”, it is disclosed that a drying film 17 is attached to the inner surface of a sealing cap layer 15 and an internal space 19 is formed between the drying film 17 and an opposed electrode 14. The solid-state drying film 17 absorbs the moisture existing inside the sealing cap layer 15, so as to prevent the generation of dark spots.
Even though the U.S. Pat. No. 5,882,761 can overcome some of the problems in the prior arts, it still has the following drawbacks:                1. The fine pattern of the organic EL device is not precise enough, thus a minute short circuit may occur between the two electrodes, leading to undesirable display cross-talk.        2. The sealing cap layer is not resistant to any possible external force because it covers the substrate without a supporting member, making the organic EL device easily damaged.        3. In spite of the full-color luminescence capability, the organic EL device is limited in its applications.        
Therefore, there is need in providing an improved organic EL device with simplified manufacturing processing, high precision, high durability, excellent resistance to external force, negligibly low dark spot generation and excellent luminescence quality.